On 23 June 2011 15:37, Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx> wrote: > On Tue, Jun 21, 2011 at 11:26:27AM +0200, Per Forlin wrote: >> Here are the results. > > It looks like this patch is either a no-op or slightly worse. As > people have been telling me that dsb is rather expensive, and this > patch results in less dsbs, I'm finding these results hard to believe. > It seems to be saying that dsb is an effective no-op on your platform. > The result of your patch depends on the number of sg-elements. With your patch there is only on DSB per list instead of element I can write a test to measure performance per number of sg-element in the sg-list. Fixed transfer size but vary the number of sg-elements in the list. This test may give a better understanding of the affect. I have seen performance gain if using __raw_write instead of writel. Writel test includes both the cost of DSB and the outer_sync, where outer_sync is more expensive one I presume. > So either people are wrong about dsb being expensive, the patch is > wrong, or there's something wrong with these results/test method. > > You do have an error in the ported patch, as that hasn't updated the > v7 cache cleaning code to remove the dsb() there, but that would only > affect the write tests. > I will fix that mistake and also improve the test cases to measure the cost per number of sg-elements. I'll come back with new numbers on Monday. Regards, Per -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
